# 271\. Encode and Decode Strings

## Method 1

input = ["hello", "world!"]
output = 5 $ hello 6 $ world!
From "0th" to "just before $", is the number of chars.
So we can know number of chars after $ as one segment and the next starting point.
Then, the problem repeats itself.

## Method 2

If we know max length of a segment, we can fix number of chars to represent the segment length.
input = ["hello", "world!"]
output = 005 hello 006 world!
The first three char is for length, not segment itself.
Skip 3 chars for number and then skip 5 chars for segment. We now have 006world!. Now the problem repeats itself.

## Method 3

https://leetcode.com/problems/encode-and-decode-strings/discuss/70402/Java-with-%22escaping%22

{"abc", "def"}    =>  "abc # def # "
{'abc', '#def'}   =>  "abc # ##def # "
{'abc##', 'def'}  =>  "abc#### # def # "

class Codec:
    def encode(self, strs: List[str]) -> str:
        """Encodes a list of strings to a single string.
        """
        return ''.join([str(len(s)) + "$" + s for s in strs])
            

    def decode(self, s: str) -> List[str]:
        """Decodes a single string to a list of strings.
        """
        result = []
        start_of_count = 0
        while start_of_count < len(s):
            length_of_count = 1
            while (start_of_count + length_of_count < len(s) and
                   s[start_of_count + length_of_count] != "$"):
                length_of_count += 1
            poisiton_of_dollar = start_of_count + length_of_count
            count = int(s[start_of_count:poisiton_of_dollar])
            start_of_text = poisiton_of_dollar + 1
            text = s[start_of_text:start_of_text + count]
            
            result.append(text)
        
            start_of_count = start_of_text + count
            
        return result

# Your Codec object will be instantiated and called as such:
# codec = Codec()
# codec.decode(codec.encode(strs))


class Codec:
    def encode(self, strs: List[str]) -> str:
        """Encodes a list of strings to a single string.
        """
        return ''.join([str(len(s)).zfill(3) + s for s in strs])
            

    def decode(self, s: str) -> List[str]:
        """Decodes a single string to a list of strings.
        """
        result = []
        start_of_segment= 0
        while start_of_segment < len(s):
            number = int(s[start_of_segment:start_of_segment + 3])
            next_start_of_segment = start_of_segment + 3 + number
            
            text = s[start_of_segment + 3: next_start_of_segment]
            result.append(text)
            start_of_segment = next_start_of_segment
        return result
    

"""
https://leetcode.com/problems/encode-and-decode-strings/discuss/70402/Java-with-%22escaping%22
"""
class Codec:
    def encode(self, strs: List[str]) -> str:
        """Encodes a list of strings to a single string.
        """
        for i, s in enumerate(strs):
            strs[i] = s.replace("#", "##")
        return '_#_'.join(strs)
            

    def decode(self, s: str) -> List[str]:
        """Decodes a single string to a list of strings.
        """
        result = s.split("_#_")
        for i, x in enumerate(result):
            result[i] = x.replace("##", "#", -1)
        return result